CHICAGO—Frigid, subzero temperatures and winter weather descended across a wide swath of the central and eastern United States on Sunday, with temperatures expected to plummet further overnight.

Some Midwestern residents were digging out from nearly a foot of snow that fell by Sunday afternoon, and grocery stores there sold out of essentials. Hazardous travel conditions in many states led to canceled flights and prompted warnings from transportation officials that only those who absolutely need to venture out should do so. Some schools canceled Monday classes, and local governments and charities worked to be sure shelters were available for anyone who needed them.

People wait for a bus at a bus stop in downtown Chicago on Sunday, Jan. 5, 2014. Sunday night temperatures will drastically drop to about minus 20 degrees. ((AP Photo/Nam Y. Huh))

Even the South will be affected by the "polar vortex" of cold air, with temperatures there set to fall well below normal on Monday and Tuesday.

FLORIDA

Temperatures are expected to dip into the 30s in parts of Florida on Tuesday, but the state's citrus industry isn't expecting any damage to crops. A spokesman for Florida Citrus Mutual said it must be at 28 degrees or lower for four hours straight for fruit to freeze badly.

ILLINOIS

Chicago Public School officials on Sunday reversed course, canceling classes for Monday ahead of the expected bitterly cold temperatures. The change in plans comes after withering criticism from the Chicago Teachers Union, though officials said they made the decision after they "evaluated the situation again.

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" Temperatures were expected to dip to minus 15 degrees on Monday, with wind chills of 40 to 50 below zero possible. The city was also walloped by snow on Sunday.

INDIANA

A winter storm had dropped nearly a foot of snow on parts of northern and central Indiana by Sunday evening, and the National Weather Service said totals in some areas could reach up to 14 inches. Gov. Mike Pence ordered nearly 100 Indiana National Guard members to be ready to help rescue stranded motorists, move people to shelters and assist local emergency services workers in reaching people who need medical help. The state General Assembly postponed Monday's opening of its 2014 session.

KENTUCKY

Even though the initial forecast for snow has been scaled back, flights for Monday and Tuesday were canceled at Barkley Regional Airport in Paducah. Organizations including churches and the Salvation Army were planning to open warming centers in some cities.

LOUISIANA

With two frigid nights on the way, New Orleans' city government said its freeze plan is in effect. All shelters will be open free of charge to people who need to get out of the cold. The city also encouraged residents to check on neighbors and the elderly.

MICHIGAN

The harshest winter conditions in 20 years are heading for Michigan's Lower Peninsula, with up to 15 inches of snow forecast for parts of the state by late Sunday followed by temperatures diving as low as minus 15.

MINNESOTA

The cold snap that the National Weather Service is calling "historic and dangerous" has arrived in Minnesota. Temperatures were in the single digits below zero in the Twin Cities area Sunday afternoon, and temperatures are expected to dip between 25 below and 40 below overnight, with wind chills plummeting to between 55 below and 65 below zero.

MISSOURI

Heavy snow combined with strong winds and cold created dangerous conditions Sunday in much of Missouri, prompting warnings that only those who absolutely need to venture out should do so. The state Department of Transportation said it was so cold the salt used to melt ice and snow wasn't very effective and that conditions were so bad they were endangering those driving the plows and trucks.

NEBRASKA

Officials are warning that frostbite and hypothermia are possible if Nebraska residents aren't prepared for the cold moving into the state Sunday afternoon. The Nebraska Humane Society urged pet owners to bring their animals inside.

NEW JERSEY

Weather-weary New Jersey residents got a short-lived respite Sunday, as warmer temperatures started to melt the snow and ice spawned by last week's major storm. But forecasters say frigid temperatures will return Monday night, when lows will drop to the single digits and wind chills could reach 15 degrees below zero.

TENNESSEE

Winter weather caused the cancellation and delay of flights both to and from Nashville and Memphis on Sunday. The Metro Nashville government said it was partnering with local organizations to make sure shelters were available. Some school districts have canceled classes Monday due to the forecast.

VIRGINIA

The National Weather Service has issued wind chill warnings that take effect Monday evening from the Alleghany Highlands southeast to the Virginia Piedmont, including the Roanoke and New River valleys, and areas west of the Blue Ridge. Those areas could see wind chills of minus 30 degrees.

WISCONSIN

Wisconsin braced Sunday for what the National Weather Service said will be the state's coldest weather since February 1996. Wind chills are expected to plummet to between 35 below to 60 below across the state by Monday morning.